With the recent popularization of computers, an inkjet printer is widely used for printing letters or an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of jetting out a liquid droplet by applying a pressure using a piezoelectric element, a system of jetting out a liquid droplet by generating a bubble in an ink under heat, a system of using an ultrasonic wave, and a system of ejecting a liquid droplet by drawing with an electrostatic force. The ink composition used for such inkjet recording includes an aqueous ink, an oily ink and a solid (fusion-type) ink. Among these inks, the aqueous ink becomes mainstream in view of production, handleability, odor, safety and the like.
The coloring agent used in such an ink for inkjet recording method is required to have high solubility in a solvent, enable high-density recording, provide good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing property and less bleeding on an image-receiving material, provide an ink having excellent storability, show no toxicity, have high purity, and be available at a low cost. However, it is very difficult to find out a coloring agent satisfying these requirements in a high level. Various dyes and pigments for inkjet recording method have been already proposed and actually used, however, a coloring agent satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments having a Colour Index (C.I.) number can hardly satisfy both color hue and fastness required of the ink for inkjet recording method. Heretofore, studies have been made on a dye having good color hue and fastness with an attempt to develop a dye excellent as the coloring agent for inkjet recording. Particularly, a dye having good color hue and excellent fastness to ozone is highly desired.
On the other hand, many dyes are difficult to dissolve in water and readily precipitate, and it has been found that a problem in that when printed, an abnormal printed part (a failure in that a bronze part, i.e., a matted surface is formed as compared with a normal printed part) resulting from aggregation of dye in a high-density printed part is produced to deteriorate the image quality. The bronze part is readily generated particularly in a multicolor mixed part.
A method of increasing an amount of a water-soluble organic solvent used so as to prevent the precipitation of dye is not preferred, because the ejection property is worsened due to increase in the viscosity and the light fastness also tends to be worsened. A method of using a dye having high light absorbance in a low concentration may be considered, but a dye also satisfying other performances is difficult to find out in view of technique.